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DBMS BCA Unit-5 Transaction - Definition Transaction - Examples COMMIT and ROLLBACK Properties of a Transaction States of Transactions The Concurrent Transactions Transactions - Lost Updates Transactions - Unrepeatable Reads Transactions - Dirty Reads Transactions - Inconsistent Analysis Serialisable Schedule Serial and Interleaved Schedule Precedence Graph Algorithm Precedence Graph Construction Non Serializable Schedule Locking Protocol Locks and Types of Locks Binary Locks Multiple-Mode Locks Shared and Exclusive Locks Two Phase Locking (2PL) Types of Two Phase Locking Database Security Goals Types of Database Security Threats to Databases Database Security & Authorization Subsystem Discretionary Security Mechanisms Mandatory Security Mechanisms Control Measures Access Control Inference Control Flow Control Data Encryption Database Security and the DBA DBA - Privileged Commands DBA Role Access Control, User Accounts and Database Audits System Log Database Audit Audit Trail Sensitive Data and Types of Disclosures Sensitive Data - Classification Factors Factors - Data is Safe Discretionary Access Control in a Database Account Level Privileges Relation Level Privileges Access Matrix Model Privileges on Relations


Shared and Exclusive Locks

Properties of shared and exclusive locks:
  • Shared Lock or Read Lock
    • It is requested by transaction that wants to just read the value of data items.
    • A shared lock on a data item does not allow an exclusive lock to be placed but permits any number of shared locks to be placed on that item.
  • Exclusive Lock
    • It is requested by a transaction on a data item that it needs to update.
    • No other transaction can place either a shared lock or an exclusive lock on a data item that has been locked in an exclusive mode.
Transactions using multiple-mode locking
Locking as above results in a serialisable schedule.